I have a DG834GT and I've been very pleased with its reliability and performance since purchase.
It's not once dropped the line in the last 3 months, and my signal is 'Good' if not 'VeryGood/Excellent' throughout my 3 bed home.
As I type from the comfort of my sofa (with 2 walls and various other obstacles in the way, using a WG111T Wireless Adapter), I'm connected at 108mbps to the network, and I'm browsing the net at max speed for my 512kbps broadband service.
I guess as there are so many hardware setup combinations, there're always going to be people with problems.
After some easy tweaking and tuning, my experienced have been very positive, however this does not invalidate your negative experience.
I hope you get it all sorted soon.